Printed circuit board and electronic device

ABSTRACT

A printed circuit board includes a printed wiring board, an electronic element provided on a mounting surface of the printed wiring board, and a heat radiation member provided on an opposite side of a side on which the printed wiring board is positioned with respect to the electronic element, the heat radiation member thermally connected to the electronic element. An end portion of the heat radiation member is disposed closer to the printed wiring board than a connection portion with the electronic element in the heat radiation member, in a state where a space is provided between the end portion and the printed wiring board.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.16/173,708 filed Oct. 29, 2018, which is based on and claims priorityunder 35 U.S.C. 119 from Japanese Patent Application No. 2017-209576filed on Oct. 30, 2017. The contents of the above applications areincorporated herein by reference.

BACKGROUND 1. Technical Field

The present invention relates to a printed circuit board and anelectronic device.

2. Related Art

In the related art, there is known a printed circuit board including aprinted wiring board, and a high heat-generating electronic element thatis mounted on the printed wiring board. As such a printed circuit board,there is known a printed circuit board including a heat radiation boardthat radiates heat which is transferred from the electronic element (forexample, see JP-A-9-17921).

In the printed circuit board disclosed in JP-A-9-17921, a metal block isbonded to an upper portion of an integrated circuit with a thermallyconductive adhesive, and a metal board as a heat radiation board isdisposed in the metal block. In such a printed circuit board, the heatwhich is generated in the integrated circuit is transferred to the metalboard through the metal block and the thermally conductive adhesive, andis radiated by the metal board, thereby, the integrated circuit iscooled.

Meanwhile, there is a case where the printed circuit board radiates anoise current which is generated in the integrated circuit or the like,as an electromagnetic wave, to an outside. In such a case, there is apossibility that a malfunction is caused in a peripheral circuit or anelectronic device. Particularly, in the printed circuit board disclosedin JP-A-9-17921, there is a problem that a noise current which isgenerated in the integrated circuit or the like is propagated to theheat radiation board, the heat radiation board serves as an antenna, theelectromagnetic wave is widely radiated on a periphery thereof, and aninfluence on a peripheral electronic device becomes large.

On the contrary, in the printed circuit board disclosed in JP-A-9-17921,the heat radiation board is connected to a signal ground of a printedsubstrate, through a conductive stud. Therefore, the noise current whichis propagated to the heat radiation board is propagated to the printedsubstrate through the stud, thereby, the electromagnetic wave isprevented from being radiated from the heat radiation board.

However, in the printed circuit board disclosed in JP-A-9-17921, sincethe heat radiation board is in a mere flat board shape, there is aproblem that the noise current is more likely to be radiated on theperiphery as an electromagnetic wave from an end portion of the heatradiation board than to be propagated to the printed substrate sidethrough the stud.

Therefore, a configuration that is capable of preventing theelectromagnetic wave from being radiated on the periphery is demanded.

SUMMARY

An advantage of some aspects of the invention is to provide a printedcircuit board that is capable of preventing an electromagnetic wave frombeing radiated to an outside.

A printed circuit board according to an aspect of the invention includesa printed wiring board, an electronic element provided on a mountingsurface of the printed wiring board, and a heat radiation memberprovided on an opposite side of a side on which the printed wiring boardis positioned with respect to the electronic element, the heat radiationmemeber thermally connected to the electronic element, in which an endportion of the heat radiation member is disposed closer to the printedwiring board than a connection portion with the electronic element inthe heat radiation member, in a state where a space is provided betweenthe end portion and the printed wiring board.

According to such a configuration, a noise current which is generated inthe electronic element to be propagated to the heat radiation member ispropagated to the printed wiring board from the end portion of the heatradiation member. Since the end portion is disposed closer to theprinted wiring board than the connection portion with the electronicelement in the heat radiation member, a distance between the end portionof the heat radiation member and the printed wiring board becomes short.Thereby, since it is possible to shorten a propagation path of the noisecurrent which is propagated to the printed wiring board from the endportion of the heat radiation member, it is possible to easily propagatethe noise current to the printed wiring board. Accordingly, it ispossible to prevent the noise current from being radiated to an outsideof the printed circuit board as an electromagnetic wave, and it ispossible to reduce an influence on a peripheral electronic device.

In the aspect, it is preferable that the end portion has a shape whichis bent toward the printed wiring. Further, in the aspect, it ispreferable that the end portion has a shape which is curved toward theprinted wiring board.

According to such a configuration, it is possible to dispose the endportion as described above, in accordance with the shape of the endportion. Accordingly, it is possible to form the heat radiation memberthat achieves effects described above, without complicating the heatradiation member.

In the aspect, it is preferable that the mounting surface and an endsurface facing the mounting surface in the end portion are parallel toeach other.

Here, in a case where the end portion does not have the end surface, anda tip of the end portion is in a shape which is sharp toward the printedwiring board side, since a facing area of a portion corresponding to thetip becomes relatively small in the printed wiring board facing the tip,the noise current which is propagated to the printed wiring board fromthe tip of the end portion of the heat radiation member becomes small.Thereby, the noise current which is not propagated to the printed wiringboard becomes the electromagnetic wave to be radiated, and there is apossibility that the electromagnetic wave which is radiated to theoutside is increased.

On the contrary, according to the configuration described above, it ispossible to increase the facing area of the portion corresponding to theend portion in the printed wiring board facing the end portion, incomparison with a case where the tip is in the shape which is sharptoward the printed wiring board. Thereby, it is possible to strengthen acoupling between the end portion of the heat radiation member and thefacing area of the printed wiring board, in the same manner as acapacitive coupling of a capacitor, and it is possible to increase thenoise current which is propagated to the printed wiring board from theend portion. Accordingly, it is possible to prevent the electromagneticwave from being radiated to the outside of the printed circuit board,and it is possible to reduce the influence on the peripheral electronicdevice.

In the aspect, it is preferable that the printed circuit board furtherincludes a heat transfer member disposed between the electronic elementand the heat radiation member.

As such a heat transfer member, it is possible to exemplify asheet-shaped heat transfer member.

According to such a configuration, it is possible to efficientlytransfer heat which is generated in the electronic element to the heatradiation member by the heat transfer member. Accordingly, it ispossible to enhance cooling efficiency of the electronic element.

In the aspect, it is preferable that the printed wiring board has aground at a position corresponding to the end portion.

According to such a configuration, it is possible to easily propagatethe noise current which heads toward the printed wiring board from theend portion of the heat radiation member to the ground of the printedwiring board. That is, it is possible to further increase the noisecurrent which is propagated to the printed wiring board from the endportion of the heat radiation member. Accordingly, it is possible toeffectively prevent the electromagnetic wave from being radiated to theoutside of the printed circuit board, and it is possible to furtherreduce the influence on the peripheral electronic device.

An electronic device according to an aspect of the invention includesthe printed circuit board according to one of the above configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a perspective view illustrating an outline of a printedcircuit board according to an embodiment of the invention.

FIG. 2 is a plan view illustrating the printed circuit board accordingto the embodiment.

FIG. 3 is a sectional view illustrating the printed circuit boardaccording to the embodiment.

FIG. 4 is a sectional view illustrating a printed circuit board in therelated art.

FIG. 5 is a sectional view illustrating Modification Example 1 of theprinted circuit board according to the embodiment.

FIG. 6 is a sectional view illustrating Modification Example 2 of theprinted circuit board according to the embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, an embodiment of the invention will be described withreference to the drawings.

Configuration of Printed Circuit Board

FIG. 1 is a perspective view illustrating a printed circuit board 1according to the embodiment, and FIG. 2 is a plan view illustrating theprinted circuit board 1. FIG. 3 is a sectional view of the printedcircuit board 1 taken along line in FIG. 2.

The printed circuit board 1 according to the embodiment is a printedcircuit board that is adopted in an electronic device or the like. Asillustrated in FIGS. 1 to 3, the printed circuit board 1 includes aprinted wiring board 2, an electronic element 3, a heat transfer member4, a heat radiation board 5, and a fixing member 6.

The printed wiring board 2 is a printed substrate which is in arectangular shape in a planar view. The printed wiring board 2 has aground layer 21 which becomes a ground in the printed circuit board 1.The ground layer 21 is provided as an inner layer on an inside of theprinted wiring board 2, and is provided up to an outside rather than aposition corresponding to an end surface 53 of the heat radiation board5 described later, in the printed wiring board 2 in the planar view.That is, the printed wiring board 2 has the ground at a positioncorresponding to an end portion 52 described later.

The electronic element 3 is an electric circuit element which uses asemiconductor as a base material. The electronic element 3 is attachedto a mounting position on a mounting surface 2A of the printed wiringboard 2.

In the electronic element 3, if an electrical current is suppliedthrough the printed wiring board 2, heat is generated due to internalcircuit resistance or the like. If a temperature of the electronicelement 3 rises to be a specified value or more due to the heatgeneration, there is concern that performance thereof is lowered or adamage is caused. Therefore, in the printed circuit board 1 according tothe embodiment, the heat which is generated in the electronic element 3is transferred to the heat radiation board 5 described later through theheat transfer member 4, and the heat is radiated by the heat radiationboards, thereby, the electronic element 3 is cooled.

In the electronic element 3, if the electrical current is suppliedthrough the printed wiring board 2, a noise current NC is generated. Ina case where the heat radiation board 5 is provided to the printedcircuit board 1 in the same manner as the embodiment, the noise currentNC is propagated to the heat radiation board 5 through the heat transfermember 4, and is radiated as an electromagnetic wave EW from the heatradiation board 5. The electromagnetic wave EW which is radiated fromthe heat radiation board 5 will be described later in detail.

The heat transfer member 4 is disposed between the electronic element 3and the heat radiation board 5, and transfers the heat to the heatradiation board 5 from the electronic element 3. In the embodiment, theheat transfer member 4 is formed of a sheet which is excellent inthermal conductivity, is flexible, and is high in adhesion. Asillustrated in FIG. 3, one surface of the heat transfer member 4 isstuck to a facing surface 31 that is a surface which is an opposite sideof a surface of a side on which the printed wiring board 2 is positionedwith respect to the electronic element 3. The other surface of the heattransfer member 4 is stuck to a surface of a side on which the printedwiring board 2 is positioned in the heat radiation board 5. Thereby, itis possible to eliminate an air layer which causes efficiency of theheat transfer to be lowered between the electronic element 3 and theheat radiation board 5, and it is possible to easily transfer the heatwhich is generated in the electronic element 3 to the heat radiationboard 5.

The heat radiation board 5 is a metal board which has a rectangularshape in the planar view, and of which a notch is provided at each offour corners. For example, the heat radiation board 5 is formed bybending end portions of four side of a sheet metal with bendingprocessing or the like. The heat radiation board 5 is thermallyconnected to the electronic element 3 through the heat transfer member4. The heat radiation board 5 is equivalent to a heat radiation member.The heat radiation board 5 is formed to be larger than the electronicelement 3, and is formed to be smaller than the printed wiring board 2,in the planar view. A direction (planar view direction of the printedwiring board 2) which is perpendicular to the mounting surface 2A of theprinted wiring board 2 is referred to as Z direction. In the Zdirection, a direction which heads to the printed wiring board 2 fromthe heat radiation board 5 is referred to +Z direction.

The heat radiation board 5 has a connection portion 55 as a portionwhich is thermally connected to the electronic element 3. Ina case wherethe printed circuit board 1 is viewed along the +Z direction, theconnection portion 55 of the heat radiation board 5 is a portion of theheat radiation board 5 corresponding to an outer shape of the electronicelement 3, or an outer shape of the member (heat transfer member 4 inthe embodiment) which is disposed between the heat radiation board 5 andthe electronic element 3. In the embodiment, the connection portion 55of the heat radiation board 5 is connected to the electronic element 3through the heat transfer member 4, but the connection portion 55 is notlimited thereto. For example, the connection portion 55 may be connectedto the electronic element 3 by being in contact directly with theelectronic element 3 without being connected through the heat transfermember 4, or may be connected to the electronic element 3 through amember other than the heat transfer member 4. For example, theconnection portion 55 may be connected to the electronic element 3through the heat transfer member 4 and the member other than the heattransfer member 4, that is, two or more members.

As illustrated in FIG. 3, the end portion 52 of the heat radiation board5 is disposed closer to the printed wiring board 2 than the connectionportion 55 with the electronic element 3 in the heat radiation board 5,in a state where a space S is provided between the end portion 52 andthe printed wiring board 2. In other words, in the heat radiation board5, the end portions 52 of four sides which are positioned on the outsideof the electronic element 3 in a case where the printed circuit board 1is viewed along the +Z direction, are disposed closer to the printedwiring board 2 than the facing surface 31 of the electronic element 3.

In detail, in a case where the printed circuit board 1 is viewed alongthe +Z direction, the heat radiation board 5 has a deformation portion51 which is bent to the printed wiring board 2, in a portion whichreaches to an outer periphery of the heat radiation board 5 from theconnection portion 55. That is, the end portion 52 has a shape that isbent to the printed wiring board 2. In a case where the heat radiationboard 5 is attached to the printed wiring board 2, the end portion 52 ofthe heat radiation board 5 is disposed closer to the printed wiringboard 2 than the connection portion 55, due to the deformation portion51. That is to say, the end portion 52 of the heat radiation board 5 isdisposed at a position which is closer to the printed wiring board 2than the connection portion 55 with the electronic element 3 in the heatradiation board 5, in the direction (Z direction) which is perpendicularto the mounting surface 2A of the printed wiring board 2, in the statewhere the space S is provided between the end portion 52 and the printedwiring board 2.

The end portion 52 has the end surface 53 on a tip side. In theembodiment, the heat radiation board 5 is provide with the deformationportion 51, thereby, the end surface 53 and the mounting surface 2A ofthe printed wiring board 2 are disposed to face each other. Asillustrated in FIG. 3, the end surface 53 facing the mounting surface 2Ais substantially parallel to the mounting surface 2A. At this time, thespace S is formed between the end surface 53 and the mounting surface2A, as described above. In other words, the heat radiation board 5 isattached to the printed wiring board 2 such that a gap is formed betweenthe end surface 53 and the mounting surface 2A. That is, the space S isprovided, thereby, the end portion 52 of the heat radiation board 5 andthe printed wiring board 2 are not in contact physically with eachother.

A case where the end surface 53 and the mounting surface 2A aresubstantially parallel to each other not only includes a scope which isrecognizable as parallel, but also includes a case of being fullyparallel to each other.

The fixing member 6 is a fastening tool which has conductivity, and ismade of a metal, and the heat radiation board 5 is attached to theprinted wiring board 2. In the embodiment, the fixing members 6 areprovided as four. Each fixing member 6 has a shaft member 61 that isinserted into each of four hole portions 54 which are formed in thevicinity of four corners of the heat radiation board 5, along+Zdirection, and a biasing member 62 that is provided with the shaftmember 61.

The shaft member 61 is inserted through the hole portion 54 of the heatradiation board 5, and is fixed to an insertion hole 22 that is formedin the printed wiring board 2. When the shaft member 61 is inserted intothe hole portion 54 of the heat radiation board 5, the shaft member 61has a head portion 611 that is positioned on the opposite side of theprinted wiring board 2 side with respect to the heat radiation board 5.Therefore, the biasing member 62 is disposed between the head portion611 and the heat radiation board 5.

In the embodiment, the biasing member 62 is formed of a compression coilspring, and biases the heat radiation board 5 toward the printed wiringboard 2 side. Due to the biasing member 62, the heat radiation board 5is fastened to the heat transfer member 4, and the heat transfer member4 is fastened to the electronic element 3. Therefore, it is possible toeasily propagate the heat which is generated in the electronic element 3to the heat radiation board 5.

Since the insertion hole 22 is connected to the ground layer 21, aportion of the noise current NC which is propagated to the heatradiation board 5 from the electronic element 3 is propagated to theprinted wiring board 2 through the fixing member 6. However, the noisecurrent which is propagated to the printed wiring board 2 through thefixing member 6 is smaller than the noise current which is propagated upto the end portion 52 of the heat radiation board 5. Therefore, even ina case where the printed circuit board 1 is configured to include thefixing member 6, there is a concern that the electromagnetic wave EW isradiated to the outside from the end portion 52 of the heat radiationboard 5.

Flow of Noise Current NC Propagating Through Printed Circuit Board

FIG. 4 is a sectional view illustrating a printed circuit board 100 inthe related art.

Here, a propagation path of the noise current NC in the printed circuitboard 100 of the related art will be described. The noise current NC isindicated by an arrow of a solid line in FIG. 4.

As illustrated in FIG. 4, the printed circuit board 100 has a printedwiring board 200, an electronic element 300, a heat transfer member 400,a heat radiation board 500, and a fixing member 600. The heat radiationboard 500 does not have the deformation portion 51 in the embodiment ofthe invention, and is formed as a flat board of a rectangular shape.That is, an end surface 530 of an end portion 520 in the heat radiationboard 500 is substantially perpendicular to a mounting surface 200A ofthe printed wiring board 200, differently from the end surface 53 of theend portion 52 in the embodiment of the invention. That is to say, theend surface 530 is formed to be disposed along the Z direction.Furthermore, the heat radiation board 500 has a connection portion 550as a portion that is thermally connected to the electronic element 300through the heat transfer member 400. In the printed circuit board 100,the end portion 520 of the heat radiation board 500 is disposed at aposition which is distant from the printed wiring board 200 rather thanthe connection portion 550, or at a position of which distances from theprinted wiring board 200 are approximately the same, in the Z directionbeing a direction which is perpendicular to the mounting surface 200A ofthe printed wiring board 200.

In the printed circuit board 100, a portion of the noise current NCwhich is generated in the electronic element 300 to be propagated to theheat radiation board 500, is propagated to the printed wiring board 200,as illustrated in FIG. 4. However, in the printed circuit board 100,since the distance between the end portion 520 and the mounting surface200A of the printed wiring board 200, that is, the distance between theend surface 530 and the mounting surface 200A is relatively long, thepropagation path of the noise current NC which is propagated to theprinted wiring board 200 from the heat radiation board 500 becomes long.Therefore, the noise current NC which heads to the printed wiring board200 from the end surface 530 is hardly likely to be propagated to theprinted wiring board 200, and a portion of the noise current NC isradiated to the outside of the printed circuit board 100 as anelectromagnetic wave EW. The electromagnetic wave EW is indicated by anarrow of a two-dot chain line in FIG. 4.

In this manner, since the electromagnetic wave EW which is radiated fromthe end surface 530 of the heat radiation board 500 is likely to bepropagated to a peripheral electronic device, an influence on theperipheral electronic device becomes large.

On the contrary, in the printed circuit board 1 according to theembodiment, the noise current NC which is generated in the electronicelement 3 is propagated to the heat radiation board 5 through the heattransfer member 4. As described above, the noise current NC which ispropagated to the heat radiation board 5, is propagated to the printedwiring board 2 from the end portion 52. At this time, since thedeformation portion 51 is bent to the printed wiring board 2, the endportion 52 of the heat radiation board 5 is disposed closer to theprinted wiring board 2 (mounting surface 2A) than the connection portion55 with the electronic element 3 in the heat radiation board 5. Thereby,since the distance between the end portion 52 (end surface 53) and themounting surface 2A of the printed wiring board 2 becomes short, and itis possible to shorten the propagation path of the noise current NCwhich is propagated to the printed wiring board 2 from the heatradiation board 5, it is possible to easily propagate the noise currentNC which is propagated to the heat radiation board 5 from the electronicelement 3, to the printed wiring board 2 from the end surface 53.Accordingly, it is possible to prevent the noise current NC from beingradiated to the outside as an electromagnetic wave EW from the printedcircuit board 1, and it is possible to reduce the influence on theperipheral electronic device.

Here, the end surface 53 is substantially parallel to the mountingsurface 2A. Thereby, for example, it is possible to increase a facingarea of a portion corresponding to the end portion 52 in the printedwiring board 2 facing the end portion 52, in comparison with a casewhere the tip of the end portion 52 is in a shape which is sharp towardthe printed wiring board 2 (mounting surface 2A) side. Thereby, it ispossible to strengthen a coupling between the end portion 52 of the heatradiation board 5 and the facing area of the printed wiring board 2, inthe same manner as a capacitive coupling of a capacitor, and it ispossible to increase the noise current NC which is propagated to theprinted wiring board 2 from the end portion 52. Accordingly, it ispossible to prevent the electromagnetic wave EW from being radiated tothe outside of the printed circuit board 1, and it is possible to reducethe influence on the peripheral electronic device.

The printed wiring board 2 has the ground layer 21 at the positioncorresponding to the end surface 53 of the heat radiation board 5.Thereby, it is possible to easily propagate the noise current NC whichheads to the printed wiring board 2 from the end portion 52 of the heatradiation board 5, to the ground layer 21 of the printed wiring board 2.Accordingly, it is possible to effectively prevent the electromagneticwave EW from being radiated to the outside of the printed circuit board1, and it is possible to further reduce the influence on the peripheralelectronic device.

Furthermore, there is a case where the electromagnetic wave which isradiated from the peripheral electronic device, as a noise current, ispropagated to the printed circuit board 1 of which the heat radiationboard 5 serves as an antenna. In this case, the noise current which ispropagated to the heat radiation board 5 is propagated to the groundlayer 21 of the printed wiring board 2 from the end surface 53 of theheat radiation board 5, as described above. Thereby, it is possible toprevent the electromagnetic wave which is radiated from the peripheralelectronic device from being propagated to the electronic element 3, andit is possible to reduce the influence on the electronic element 3 dueto the electromagnetic wave which is radiated from the peripheralelectronic device.

Effect of Embodiment

According to the printed circuit board 1 of the embodiment describedabove, the following effects are obtained.

In the printed circuit board 1, the end surface 53 of the heat radiationboard 5 is disposed closer to the printed wiring board 2 (mountingsurface 2A) than the connection portion 55 of the heat radiation board5, in the state where the space S is provided between the end surface 53and the printed wiring board 2. Thereby, since it is possible to shortenthe propagation path of the noise current NC which is propagated to theprinted wiring board 2 from the heat radiation board 5, it is possibleto easily propagate the noise current NC to the printed wiring board 2from the end surface 53 in the heat radiation board 5. Accordingly, itis possible to prevent the electromagnetic wave EW from being radiatedto the outside from the printed circuit board 1, and it is possible toreduce the influence on the peripheral electronic device.

Since the end portion 52 has the shape which is bent to the printedwiring board 2, it is possible to dispose the end portion 52 asdescribed above. Accordingly, it is possible to form the heat radiationboard 5 that achieves the effects described above, without complicatingthe heat radiation board 5.

The end surface 53 is substantially parallel to the mounting surface 2A.According thereto, since it is possible to increase the facing area ofthe portion facing the end surface 53 of the heat radiation board 5 inthe mounting surface 2A, it is possible to increase the noise current NCwhich is propagated to the printed wiring board 2 from the end surface53 of the heat radiation board 5. Accordingly, it is possible to preventthe electromagnetic wave EW from being radiated to the outside of theprinted circuit board 1, and it is possible to reduce the influence onthe peripheral electronic device.

The printed wiring board 2 has the ground layer 21 at the positioncorresponding to the end surface 53 of the heat radiation board 5.Thereby, it is possible to easily propagate the noise current NC whichheads to the printed wiring board 2 from the end portion 52 of the heatradiation board 5, to the ground layer 21 of the printed wiring board 2,and it is possible to effectively prevent the electromagnetic wave EWfrom being radiated to the outside of the printed circuit board 1.

There is a case where the electromagnetic wave which is radiated fromthe peripheral electronic device, as a noise current, is propagated tothe printed circuit board 1 of which the heat radiation board 5 servesas an antenna, but the noise current is propagated to the ground layer21 of the printed wiring board 2 from the end surface 53 of the heatradiation board 5. Thereby, it is possible to prevent theelectromagnetic wave which is radiated from the peripheral electronicdevice from being propagated to the electronic element 3.

The heat transfer member 4 is stuck to the facing surface 31 of theelectronic element 3 and the heat radiation board 5. Thereby, it ispossible to eliminate the air layer between the electronic element 3 andthe heat radiation board 5, and it is possible to easily transfer theheat which is generated in the electronic element 3 to the heatradiation board 5.

Modification of Embodiment

The invention is not limited to the embodiment described above, and theinvention includes a case of being modified or improved within the scopewhich is capable of achieving the advantage of some aspects of theinvention.

In the embodiment described above, the heat radiation board 5 has thebent deformation portion 51 which is bent to the printed wiring board 2,in the portion which reaches to the outer periphery of the heatradiation board 5 from the connection portion 55. However, the shape ofthe heat radiation board 5 is not limited thereto, and the shape thereofmay be other shapes.

FIG. 5 is a sectional view illustrating a printed circuit board 1B asModification Example 1 of the heat radiation board 5, and FIG. 6 is asectional view illustrating a printed circuit board 1C as ModificationExample 2.

For example, a heat radiation board 5B illustrated in FIG. 5, and a heatradiation board 5C illustrated in FIG. 6 are metal boards which have therectangular shapes in the planar view, and of which the notch isprovided at each of four corners, in the same manner as the heatradiation board 5 described above. That is, the heat radiation boards 5Band 5C are equivalent to the heat radiation members. However, the heatradiation board 5B illustrated in FIG. 5 has a deformation portion 51Bthat is curved to the printed wiring board 2, in a portion which reachesto the outer periphery of the heat radiation board 5B from a connectionportion 55B of the heat radiation board 5B. That is to say, an endportion 52B of the heat radiation board 5B has a shape which is curvedto the printed wiring board 2. The heat radiation board 5B is providedwith the deformation portion 51B, thereby, an end surface 53B and themounting surface 2A of the printed wiring board 2 are disposed to faceeach other.

In this manner, the end portion 52B of the heat radiation board 5B isdisposed closer to the printed wiring board 2 than the connectionportion 55B of the heat radiation board 5B, in a state where the space Sis provided between the end portion 52B and the printed wiring board 2,in the same manner as the end portion 52 described above. Even with sucha heat radiation board 5B, it is possible to achieve the effects whichare the same as those of the heat radiation board 5.

The heat radiation board 5C illustrated in FIG. 6 has a bent deformationportion 51C1 that is bent to the printed wiring board 2 (mountingsurface 2A), in a portion which reaches to the outer periphery of theheat radiation board 5C from a connection portion 55C of the heatradiation board 5C, and a bent deformation portion 51C2 that is bent toan opposite side (outside of the printed circuit board 1C) of a side onwhich the electronic element 3 is positioned with respect to thedeformation portion 51C1. For the second time, a tip side (end portion52C side) of the deformation portion 51C1 is bent to a direction whichis along the mounting surface 2A of the printed wiring board 2. Thedeformation portions 51C1 and 51C2 are provided with the heat radiationboard 5C, thereby, an end surface 53C and the mounting surface 2A of theprinted wiring board 2 are disposed without facing each other, such thatthe end surface 53C is along the Z direction.

In this manner, the end portion 52C of the heat radiation board 5C isdisposed closer to the printed wiring board 2 than the connectionportion 55C of the heat radiation board 5C, such that the end surface53C does not face the printed wiring board 2, in a state where the spaceS is provided between the end portion 52C and the printed wiring board2, in the same manner as the end portion 52 described above. Thedeformation portion 51C2 is provided, thereby, the facing area in themounting surface 2A facing the surface which is parallel to the mountingsurface 2A of the printed wiring board 2 in the deformation portion 51C2becomes relatively large. Even with such a heat radiation board 5C, itis possible to achieve the effects which are the same as those of theheat radiation board 5.

In the embodiment described above and each Modification Exampledescribed above, the end portions 52, 52B, and 52C of four sides in theheat radiation boards 5, 5B, and 5C are configured to be respectivelydisposed closer to the printed wiring board 2 than the connectionportions 55, 55B, and 55C, in the state where the space S is providedbetween the end portion and the printed wiring board 2, but theconfiguration thereof is not limited thereto. The configuration thereofmay be any configuration so long as at least one of the end portions offour sides in each heat radiation board has such a configuration. Theheat radiation boards 5, 5B, and 5C are not limited to the shape havingthe rectangular shape in the planar view, and may have any shape so longas the shape thereof is a shape having at least one end portion.

In the embodiment described above and each Modification Exampledescribed above, each of the end surfaces 53, 53B, and 53C issubstantially parallel to the mounting surface 2A. However, theconfiguration thereof is not limited thereto. For example, a portion ofthe end surfaces 53, 53B, and 53C may protrude in a tapered shape. Aconcave portion may be provided in a portion of the end surfaces 53,53B, and 53C.

In the embodiment described above and each Modification Exampledescribed above, the heat transfer member 4 is formed of the sheet whichis flexible, and is high in adhesion. However, the configuration thereofis not limited thereto. For example, a heat transfer grease may beapplied between the electronic element 3 and the heat radiation board 5,in replacement of the heat transfer member 4. The invention alsoincludes a configuration in which the heat transfer member is notdisposed between the electronic element 3 and the heat radiation board5.

In the embodiment described above and each Modification Exampledescribed above, the ground layer 21 is provided at the positioncorresponding to each end surface of the heat radiation board 5, 5B, and5C, on the inside of the printed wiring board 2. However, theconfiguration thereof is not limited thereto, and may be anyconfiguration so long as the ground is provided even at the positioncorresponding to each of the end surfaces 53, 53B, and 53C of theprinted wiring board 2. For example, the ground may be provided in aportion of the position corresponding to each of the end surfaces 53,53B, and 53C. The ground may be positioned on a surface layer of theprinted wiring board 2.

In the embodiment described above and each Modification Exampledescribed above, the fixing member 6 attaches the heat radiation boards5, 5B, and 5C respectively to the printed wiring board 2. However, theconfiguration thereof is not limited thereto. For example, the heatradiation boards 5, 5B, and 5C may be attached to the printed wiringboard 2 by a screw or the like. The heat radiation boards 5, 5B, and 5Cmay be attached to the electronic element 3 by the screw or the like.

In the embodiment described above and each Modification Exampledescribed above, the fixing members 6 are provided as four. However, theconfiguration thereof is not limited thereto, and three or less fixingmembers 6 may be provided, and five or more fixing members 6 may beprovided.

In the embodiment described above and each Modification Exampledescribed above, the biasing member 62 is disposed between the headportion 611 of the fixing member 6 and each of the heat radiation boards5, 5B, and 5C. However, the configuration thereof is not limitedthereto. For example, in the shaft member 61, the biasing member 62 maybe disposed between the heat radiation board 5 and the printed wiringboard 2. The invention also includes a configuration in which thebiasing member is not disposed in the fixing member 6.

In the embodiment described above and each Modification Exampledescribed above, one electronic element 3 is mounted on the mountingsurface 2A of the printed wiring board 2. However, the configurationthereof is not limited thereto, and it is possible to suitably changethe number of electronic elements 3 which are mounted on the mountingsurface 2A. At this time, the heat radiation board 5 may be provided inaccordance with one electronic element 3, or the heat radiation board 5may be provided to be connected to each of a plurality of electronicelements 3. The invention also includes a configuration in which theheat radiation board 5 is provided in accordance with at least oneelectronic element 3 on the mounting surface 2A, and the heat radiationboard is not provided in other electronic elements 3.

The entire disclosure of Japanese Patent Application No. 2017-209576,filed Oct. 30, 2017 is expressly incorporated by reference herein.

What is claimed is:
 1. A printed circuit board comprising: a printedwiring board; an electronic element provided on amounting surface of theprinted wiring board; and a heat radiation member provided on anopposite side of a side on which the printed wiring board is positionedwith respect to the electronic element, the heat radiation memberthermally connected to the electronic element, wherein a surface facingthe printed wiring board in an end portion of the heat radiation memberis disposed closer to the printed wiring board than a connection portionwith the electronic element in the heat radiation member, in a statewhere a space is provided between the end portion and the printed wiringboard such that the surface facing the printed wiring board is not indirect contact with the printed wiring board and such that a propagationpath of noise current which is propagated to the printed wiring boardfrom the heat radiation member shortens.
 2. The printed circuit boardaccording to claim 1, wherein the end portion has a shape which is benttoward the printed wiring board.
 3. The printed circuit board accordingto claim 1, wherein the end portion has a shape which is curved towardthe printed wiring board.
 4. The printed circuit board according toclaim 1, wherein the mounting surface and the surface facing the printedwiring board in the end portion are parallel to each other.
 5. Theprinted circuit board according to claim 1, further comprising: a heattransfer member disposed between the electronic element and the heatradiation member.
 6. The printed circuit board according to claim 1,wherein the printed wiring board has a ground at a positioncorresponding to the surface facing the printed wiring board in the endportion.
 7. The printed circuit board according to claim 1, furthercomprising: a heat transfer member disposed between the electronicelement and the heat radiation member and having an end portion that isa surface that is not in contact with the electronic element and theheat radiation member, wherein the end portion of the heat transfermember is not indirect contact with the end portion of the heatradiation member.
 8. An electronic device comprising: the printedcircuit board according to claim 1.